Add correct error message on unknown parameter

src/utictactoe.c

@@ -127,7 +127,7 @@ int main(int argc, char* argv[]) {
             exit(EXIT_SUCCESS);
         
         default:
-            fprintf(stderr, "Error: unknown option");
+            fprintf(stderr, "Try `utictactie --help' for more information.\n");
             exit (EXIT_FAILURE);
         }
     }